A numerical model based on the Kampmann and Wagner method was
developed to predict the evolution of precipitate distribution in 7xxx aluminium alloy
during non-isothermal heat treatments. The model considers the nucleation, growth
and coarsening/dissolution of the metastable and equilibrium precipitate phases, η'
and η with their stochiometric composition, MgZn2. Constitutive model equations for
nucleation were based on the classical theory of nucleation whilst growth and
coarsening were treated using classical phase transformation theory. The transition
between η' and η, where η' acts as a precursor for η was also accounted for in the
model. Differential scanning calorimetry was used to calibrate the homogeneous
precipitation kinetics. The model also predicts the evolution of grain boundary
precipitates and their effect on precipitate free zone size. Jominy end quench tests
were performed to calibrate grain boundary precipitation kinetics. Precipitation on
dislocations and dispersoids was considered. The dislocation and dispersoid densities
were varied to represent different regions of a grain and therefore account for the
spatial distribution of preferential heterogeneous precipitation sites. Comparison
between the model prediction and experimental characterisation of the microstructure
evolution of a friction stir welded 7449 aluminium alloy was found to be reasonably
consistent.